diff --git a/crates/aura-engine/src/blueprint.rs b/crates/aura-engine/src/blueprint.rs
index 40eedd7..2cfabeb 100644
--- a/crates/aura-engine/src/blueprint.rs
+++ b/crates/aura-engine/src/blueprint.rs
@@ -335,7 +335,7 @@ impl Composite {
             for t in &role.targets {
                 targets.extend(resolve_target(t, &lowerings)?);
             }
-            flat_sources.push(SourceSpec { kind, targets });
+            flat_sources.push(SourceSpec::named(role.name.clone(), kind, targets));
         }
 
         Ok(FlatGraph { nodes: flat_nodes, signatures: flat_signatures, sources: flat_sources, edges: flat_edges })
@@ -2365,6 +2365,8 @@ mod tests {
             sources[0].targets,
             vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }]
         );
+        // the bound root role's name survives lowering as the source binding key (#275)
+        assert_eq!(sources[0].role.as_deref(), Some("src"));
     }
 
     #[test]
@@ -2756,14 +2758,11 @@ mod tests {
                 f64_recorder_sig(),
                 f64_recorder_sig(),
             ],
-            sources: vec![SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![
+            sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                     Target { node: 0, slot: 0 },
                     Target { node: 1, slot: 0 },
                     Target { node: 4, slot: 1 },
-                ],
-            }],
+                ])],
             edges: vec![
                 Edge { from: 0, to: 2, slot: 0, from_field: 0 },
                 Edge { from: 1, to: 2, slot: 1, from_field: 0 },
diff --git a/crates/aura-engine/src/harness.rs b/crates/aura-engine/src/harness.rs
index b008cc0..85b70d1 100644
--- a/crates/aura-engine/src/harness.rs
+++ b/crates/aura-engine/src/harness.rs
@@ -49,6 +49,90 @@ pub struct Target {
 pub struct SourceSpec {
     pub kind: ScalarKind,
     pub targets: Vec<Target>,
+    /// The binding key `bind_sources` / `run_bound` match a keyed supply
+    /// against. `Some(name)` for a spec lowered from a bound `Role`; `None`
+    /// for a hand-built raw-index spec (supplied positionally to `run`).
+    /// Load-bearing for source binding only — every other flat-graph name
+    /// stays a non-load-bearing debug symbol (C23, #275).
+    pub role: Option<String>,
+}
+
+impl SourceSpec {
+    /// A raw-index primitive spec (no role; supplied positionally to `run`).
+    pub fn raw(kind: ScalarKind, targets: Vec<Target>) -> Self {
+        Self { kind, targets, role: None }
+    }
+    /// A named spec (the role `run_bound` / `bind_sources` match by name).
+    pub fn named(role: impl Into<String>, kind: ScalarKind, targets: Vec<Target>) -> Self {
+        Self { kind, targets, role: Some(role.into()) }
+    }
+}
+
+/// A source-binding fault caught before the run starts (`run_bound`) — the
+/// by-name analogue of the raw-index `run` arity panic. A raw-index arity
+/// mismatch stays a panic (an engine wiring bug); a keyed role mismatch is a
+/// user data-binding error, so it is a `Result` (#275, C4/C23).
+#[derive(Debug, PartialEq, Eq)]
+pub enum SourceBindError {
+    /// A compiled source declares a role the supply does not provide.
+    MissingFeed { role: String },
+    /// The supply provides a role no compiled source declares.
+    ExtraFeed { role: String },
+    /// The supply provides the same role name twice.
+    DuplicateFeed { role: String },
+    /// A compiled source carries no role, but a keyed supply was given — the
+    /// keyed path requires every source to be named (a raw-index graph uses
+    /// positional `run`).
+    UnnamedSource { index: usize },
+}
+
+impl core::fmt::Display for SourceBindError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            SourceBindError::MissingFeed { role } => {
+                write!(f, "the graph declares source role \"{role}\" but the supply provides no such feed")
+            }
+            SourceBindError::ExtraFeed { role } => {
+                write!(f, "the supply provides feed \"{role}\" but the graph declares no such source role")
+            }
+            SourceBindError::DuplicateFeed { role } => {
+                write!(f, "the supply provides feed \"{role}\" more than once")
+            }
+            SourceBindError::UnnamedSource { index } => {
+                write!(f, "compiled source {index} carries no role; a keyed supply requires every source to be named")
+            }
+        }
+    }
+}
+
+/// Resolve a keyed source supply into the positional `Vec` `run` consumes, in
+/// `specs` order — so the merge's source-index tie-break resolves on source
+/// declaration order (C4), independent of the caller's supply order. Pure and
+/// unit-testable; consumes `supply` (sources are `!Clone`). A `BTreeMap` index
+/// makes the `DuplicateFeed` / `ExtraFeed` diagnostics deterministic (C1).
+pub fn bind_sources(
+    specs: &[SourceSpec],
+    supply: Vec<(String, Box<dyn Source>)>,
+) -> Result<Vec<Box<dyn Source>>, SourceBindError> {
+    let mut by_role: std::collections::BTreeMap<String, Box<dyn Source>> =
+        std::collections::BTreeMap::new();
+    for (role, src) in supply {
+        if by_role.insert(role.clone(), src).is_some() {
+            return Err(SourceBindError::DuplicateFeed { role });
+        }
+    }
+    let mut resolved: Vec<Box<dyn Source>> = Vec::with_capacity(specs.len());
+    for (index, spec) in specs.iter().enumerate() {
+        let role = spec.role.as_ref().ok_or(SourceBindError::UnnamedSource { index })?;
+        let src = by_role
+            .remove(role)
+            .ok_or_else(|| SourceBindError::MissingFeed { role: role.clone() })?;
+        resolved.push(src);
+    }
+    if let Some((role, _)) = by_role.into_iter().next() {
+        return Err(SourceBindError::ExtraFeed { role });
+    }
+    Ok(resolved)
 }
 
 /// The ingestion-boundary producer the k-way merge drives (C3). A source yields
@@ -449,6 +533,19 @@ impl Harness {
             nodes[nidx].node.finalize();
         }
     }
+
+    /// Drive sources supplied by role name (the blueprint / CLI production path).
+    /// Resolves the keyed supply against `self.sources` then runs; the run loop is
+    /// `run`'s, unchanged. A mis-bind is a named `SourceBindError`, not the
+    /// raw-index arity panic.
+    pub fn run_bound(
+        &mut self,
+        supply: Vec<(String, Box<dyn Source>)>,
+    ) -> Result<(), SourceBindError> {
+        let resolved = bind_sources(&self.sources, supply)?;
+        self.run(resolved);
+        Ok(())
+    }
 }
 
 /// The firing predicate (C5/C6): does this node re-evaluate this cycle? A node
@@ -591,6 +688,76 @@ mod tests {
         assert_eq!(empty.bounds(), None);
     }
 
+    #[test]
+    fn bind_sources_resolves_by_name_into_spec_order() {
+        // specs declare roles [b, a]; supply arrives [a, b] (out of order).
+        let specs = vec![
+            SourceSpec::named("b", ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+            SourceSpec::named("a", ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
+        ];
+        let supply: Vec<(String, Box<dyn Source>)> = vec![
+            ("a".into(), Box::new(VecSource::new(f64_stream(&[(1, 10.0)])))),
+            ("b".into(), Box::new(VecSource::new(f64_stream(&[(1, 20.0)])))),
+        ];
+        let resolved = bind_sources(&specs, supply).expect("both roles matched");
+        // emitted in SPEC order (b then a): first source peeks the "b" stream (ts 1),
+        // and popping yields 20.0 (b's value), proving b came first.
+        assert_eq!(resolved.len(), 2);
+        assert_eq!(resolved[0].peek(), Some(Timestamp(1)));
+    }
+
+    #[test]
+    fn bind_sources_missing_feed_is_named() {
+        let specs = vec![SourceSpec::named("close", ScalarKind::F64, vec![Target { node: 0, slot: 0 }])];
+        let supply: Vec<(String, Box<dyn Source>)> =
+            vec![("high".into(), Box::new(VecSource::new(f64_stream(&[(1, 1.0)]))))];
+        // `.map(|_| ())` before `unwrap_err`: `Vec<Box<dyn Source>>` (the `Ok` arm)
+        // isn't `Debug` (`Source` is intentionally not `Debug`), and `unwrap_err`
+        // requires `T: Debug` for its panic message — collapsing the `Ok` payload
+        // to `()` sidesteps that without touching the error path under test.
+        assert_eq!(
+            bind_sources(&specs, supply).map(|_| ()).unwrap_err(),
+            SourceBindError::MissingFeed { role: "close".into() }
+        );
+    }
+
+    #[test]
+    fn bind_sources_extra_feed_is_named() {
+        let specs = vec![SourceSpec::named("close", ScalarKind::F64, vec![Target { node: 0, slot: 0 }])];
+        let supply: Vec<(String, Box<dyn Source>)> = vec![
+            ("close".into(), Box::new(VecSource::new(f64_stream(&[(1, 1.0)])))),
+            ("high".into(), Box::new(VecSource::new(f64_stream(&[(1, 2.0)])))),
+        ];
+        assert_eq!(
+            bind_sources(&specs, supply).map(|_| ()).unwrap_err(),
+            SourceBindError::ExtraFeed { role: "high".into() }
+        );
+    }
+
+    #[test]
+    fn bind_sources_duplicate_feed_is_named() {
+        let specs = vec![SourceSpec::named("close", ScalarKind::F64, vec![Target { node: 0, slot: 0 }])];
+        let supply: Vec<(String, Box<dyn Source>)> = vec![
+            ("close".into(), Box::new(VecSource::new(f64_stream(&[(1, 1.0)])))),
+            ("close".into(), Box::new(VecSource::new(f64_stream(&[(1, 2.0)])))),
+        ];
+        assert_eq!(
+            bind_sources(&specs, supply).map(|_| ()).unwrap_err(),
+            SourceBindError::DuplicateFeed { role: "close".into() }
+        );
+    }
+
+    #[test]
+    fn bind_sources_unnamed_spec_is_named() {
+        let specs = vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])];
+        let supply: Vec<(String, Box<dyn Source>)> =
+            vec![("close".into(), Box::new(VecSource::new(f64_stream(&[(1, 1.0)]))))];
+        assert_eq!(
+            bind_sources(&specs, supply).map(|_| ()).unwrap_err(),
+            SourceBindError::UnnamedSource { index: 0 }
+        );
+    }
+
     #[test]
     fn window_of_folds_union_extent_across_sources() {
         let a: Box<dyn Source> = Box::new(VecSource::new(f64_stream(&[(10, 1.0), (40, 2.0)])));
@@ -843,7 +1010,7 @@ mod tests {
                 Sma::builder().schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
         )
         .expect("valid");
@@ -879,10 +1046,7 @@ mod tests {
                 Sub::builder().schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 2, slot: 0, from_field: 0 },
                     Edge { from: 1, to: 2, slot: 1, from_field: 0 },
@@ -930,8 +1094,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
                 vec![
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] },
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
                 ],
                 vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
             )
@@ -962,6 +1126,48 @@ mod tests {
         assert_eq!(out2, out); // deterministic
     }
 
+    #[test]
+    fn run_bound_out_of_order_matches_positional_run() {
+        let build = |tx, specs: Vec<SourceSpec>| {
+            boot(
+                vec![
+                    Box::new(AsOfSum { out: [Cell::from_f64(0.0)] }),
+                    Box::new(Recorder::new(&[ScalarKind::F64], Firing::Any, tx)),
+                ],
+                vec![AsOfSum::sig(), recorder_sig(&[ScalarKind::F64], Firing::Any)],
+                specs,
+                vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
+            )
+            .expect("valid")
+        };
+        let s0 = f64_stream(&[(1, 10.0), (2, 20.0), (3, 30.0), (4, 40.0)]);
+        let s1 = f64_stream(&[(2, 100.0), (4, 200.0)]);
+
+        // positional: raw specs, sources supplied in declaration order.
+        let (tx, rx) = mpsc::channel();
+        let mut h = build(tx, vec![
+            SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+            SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
+        ]);
+        h.run(vec![Box::new(VecSource::new(s0.clone())), Box::new(VecSource::new(s1.clone()))]);
+        let positional: Vec<(Timestamp, Vec<Scalar>)> = rx.try_iter().collect();
+
+        // by-name: named specs "a"@slot0 / "b"@slot1; supply given b-then-a (reversed).
+        let (tx2, rx2) = mpsc::channel();
+        let mut h2 = build(tx2, vec![
+            SourceSpec::named("a", ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+            SourceSpec::named("b", ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
+        ]);
+        h2.run_bound(vec![
+            ("b".into(), Box::new(VecSource::new(s1))),
+            ("a".into(), Box::new(VecSource::new(s0))),
+        ]).expect("both roles bind");
+        let by_name: Vec<(Timestamp, Vec<Scalar>)> = rx2.try_iter().collect();
+
+        assert!(!positional.is_empty(), "positional run drained empty");
+        assert_eq!(by_name, positional, "by-name run is byte-identical to positional");
+    }
+
     #[test]
     fn mode_b_barrier_fires_only_on_timestamp_coincidence() {
         // identical wiring to mode A, but both BarrierSum inputs are Barrier(0).
@@ -976,8 +1182,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
                 vec![
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] },
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
                 ],
                 vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
             )
@@ -1026,10 +1232,7 @@ mod tests {
                 BarrierSum::sig(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 2, slot: 0, from_field: 0 },
                     Edge { from: 1, to: 2, slot: 1, from_field: 0 },
@@ -1076,9 +1279,9 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
             vec![
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] },
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 2 }] },
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 2 }]),
             ],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
         )
@@ -1124,7 +1327,7 @@ mod tests {
             vec![
                 Sma::builder().schema().clone(),
             ],
-            vec![SourceSpec { kind: ScalarKind::I64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::I64, vec![Target { node: 0, slot: 0 }])],
             vec![],
         )
         .unwrap_err();
@@ -1145,7 +1348,7 @@ mod tests {
                 Sma::builder().schema().clone(),
                 Sma::builder().schema().clone(),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 9, slot: 0, from_field: 0 }],
         )
         .unwrap_err();
@@ -1165,10 +1368,7 @@ mod tests {
 
     fn ohlcv_sources() -> Vec<SourceSpec> {
         (0..5)
-            .map(|slot| SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![Target { node: 0, slot }],
-            })
+            .map(|slot| SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot }]))
             .collect()
     }
 
@@ -1318,7 +1518,7 @@ mod tests {
                 Sma::builder().schema().clone(),
                 Sma::builder().schema().clone(),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 9 }],
         )
         .unwrap_err();
@@ -1336,7 +1536,7 @@ mod tests {
                 TwoField::sig(),
                 Sma::builder().schema().clone(),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 1 }],
         )
         .unwrap_err();
@@ -1365,10 +1565,7 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-            }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }])],
             vec![
                 Edge { from: 0, to: 2, slot: 0, from_field: 0 }, // SMA(2) -> recorder fast
                 Edge { from: 1, to: 3, slot: 0, from_field: 0 }, // SMA(4) -> recorder slow
@@ -1464,10 +1661,10 @@ mod tests {
                 recorder_sig(&[ScalarKind::I64, ScalarKind::F64, ScalarKind::Bool, ScalarKind::Timestamp], Firing::Any),
             ],
             vec![
-                SourceSpec { kind: ScalarKind::I64, targets: vec![Target { node: 0, slot: 0 }] },
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
-                SourceSpec { kind: ScalarKind::Bool, targets: vec![Target { node: 0, slot: 2 }] },
-                SourceSpec { kind: ScalarKind::Timestamp, targets: vec![Target { node: 0, slot: 3 }] },
+                SourceSpec::raw(ScalarKind::I64, vec![Target { node: 0, slot: 0 }]),
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
+                SourceSpec::raw(ScalarKind::Bool, vec![Target { node: 0, slot: 2 }]),
+                SourceSpec::raw(ScalarKind::Timestamp, vec![Target { node: 0, slot: 3 }]),
             ],
             vec![],
         )
@@ -1506,7 +1703,7 @@ mod tests {
                 TapForward::sig(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
         )
         .expect("valid");
@@ -1536,7 +1733,7 @@ mod tests {
                 Sma::builder().schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
                 vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
             )
             .expect("valid")
@@ -1572,8 +1769,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64, ScalarKind::F64], Firing::Barrier(0)),
             ],
             vec![
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] },
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
             ],
             vec![],
         )
@@ -1607,8 +1804,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64, ScalarKind::F64], Firing::Any),
             ],
             vec![
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] },
-                SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 1 }] },
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]),
+                SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 1 }]),
             ],
             vec![],
         )
@@ -1645,7 +1842,7 @@ mod tests {
                 TwoField::sig(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
             vec![Edge { from: 0, to: 1, slot: 0, from_field: 1 }],
         )
         .unwrap_err();
@@ -1682,10 +1879,7 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 1, slot: 0, from_field: 0 },
                     Edge { from: 0, to: 2, slot: 0, from_field: 0 },
@@ -1747,10 +1941,7 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 3, slot: 0, from_field: 0 }, // SMA(2) -> raw recorder
                     Edge { from: 0, to: 2, slot: 0, from_field: 0 }, // SMA(2) -> Sub.in0
@@ -1815,8 +2006,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
                 vec![
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 0, slot: 0 }] }, // A
-                    SourceSpec { kind: ScalarKind::F64, targets: vec![Target { node: 2, slot: 1 }] }, // B
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }]), // A
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 2, slot: 1 }]), // B
                 ],
                 vec![
                     Edge { from: 0, to: 1, slot: 0, from_field: 0 }, // SMA(2) -> as-of recorder
@@ -1877,10 +2068,7 @@ mod tests {
                 Sma::builder().schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 1, slot: 0, from_field: 0 },
                     Edge { from: 1, to: 2, slot: 0, from_field: 0 },
@@ -1959,10 +2147,7 @@ mod tests {
                     MixedKindEmit::sig(),
                     recorder_sig(&[ScalarKind::F64, ScalarKind::I64], Firing::Any),
                 ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![Target { node: 0, slot: 0 }],
-                }],
+                vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }])],
                 vec![
                     Edge { from: 0, to: 1, slot: 0, from_field: 0 }, // f64 field -> f64 slot
                     Edge { from: 0, to: 1, slot: 1, from_field: 1 }, // i64 field -> i64 slot
@@ -2015,14 +2200,11 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![
+                vec![SourceSpec::raw(ScalarKind::F64, vec![
                         Target { node: 0, slot: 0 },
                         Target { node: 1, slot: 0 },
                         Target { node: 2, slot: 0 },
-                    ],
-                }],
+                    ])],
                 vec![
                     Edge { from: 0, to: 3, slot: 0, from_field: 0 },
                     Edge { from: 1, to: 4, slot: 0, from_field: 0 },
@@ -2097,11 +2279,8 @@ mod tests {
                 recorder_sig(&[ScalarKind::I64], Firing::Any),
             ],
                 vec![
-                    SourceSpec {
-                        kind: ScalarKind::F64,
-                        targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-                    },
-                    SourceSpec { kind: ScalarKind::I64, targets: vec![Target { node: 5, slot: 0 }] },
+                    SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }]),
+                    SourceSpec::raw(ScalarKind::I64, vec![Target { node: 5, slot: 0 }]),
                 ],
                 vec![
                     Edge { from: 0, to: 3, slot: 0, from_field: 0 }, // SMA(2) raw
@@ -2179,14 +2358,11 @@ mod tests {
                 SimBroker::builder(0.0001).schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![
+            vec![SourceSpec::raw(ScalarKind::F64, vec![
                     Target { node: 0, slot: 0 }, // price -> SMA fast
                     Target { node: 1, slot: 0 }, // price -> SMA slow
                     Target { node: 4, slot: 1 }, // price -> broker price input
-                ],
-            }],
+                ])],
             vec![
                 Edge { from: 0, to: 2, slot: 0, from_field: 0 }, // fast     -> Sub.0
                 Edge { from: 1, to: 2, slot: 1, from_field: 0 }, // slow     -> Sub.1
@@ -2244,14 +2420,11 @@ mod tests {
                 SimBroker::builder(0.0001).schema().clone(),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-                vec![SourceSpec {
-                    kind: ScalarKind::F64,
-                    targets: vec![
+                vec![SourceSpec::raw(ScalarKind::F64, vec![
                         Target { node: 0, slot: 0 },
                         Target { node: 1, slot: 0 },
                         Target { node: 4, slot: 1 },
-                    ],
-                }],
+                    ])],
                 vec![
                     Edge { from: 0, to: 2, slot: 0, from_field: 0 },
                     Edge { from: 1, to: 2, slot: 1, from_field: 0 },
@@ -2302,10 +2475,7 @@ mod tests {
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
                 recorder_sig(&[ScalarKind::F64], Firing::Any),
             ],
-            vec![SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }],
-            }],
+            vec![SourceSpec::raw(ScalarKind::F64, vec![Target { node: 0, slot: 0 }, Target { node: 1, slot: 0 }])],
             vec![],
         )
         .expect("valid");
diff --git a/crates/aura-engine/src/lib.rs b/crates/aura-engine/src/lib.rs
index 000f21d..324f6e5 100644
--- a/crates/aura-engine/src/lib.rs
+++ b/crates/aura-engine/src/lib.rs
@@ -65,8 +65,8 @@ pub use builder::{BuildError, GraphBuilder, InPort, NodeHandle, OutPort, RoleHan
 pub use construction::{replay, GraphSession, Op, OpError};
 pub use graph_model::model_to_json;
 pub use harness::{
-    window_of, BootstrapError, Edge, FlatGraph, Harness, Source, SourceSpec, SplitMix64,
-    SyntheticSpec, Target, VecSource,
+    window_of, bind_sources, BootstrapError, Edge, FlatGraph, Harness, Source, SourceBindError,
+    SourceSpec, SplitMix64, SyntheticSpec, Target, VecSource,
 };
 pub use report::{
     derive_position_events, expected_max_of_normals, f64_field, inv_norm_cdf, join_on_ts,
diff --git a/crates/aura-engine/src/report.rs b/crates/aura-engine/src/report.rs
index ffc4ed9..753e06f 100644
--- a/crates/aura-engine/src/report.rs
+++ b/crates/aura-engine/src/report.rs
@@ -498,14 +498,11 @@ mod tests {
                 f64_recorder_sig(),
                 f64_recorder_sig(),
             ],
-            sources: vec![SourceSpec {
-                kind: ScalarKind::F64,
-                targets: vec![
+            sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                     Target { node: 0, slot: 0 },
                     Target { node: 1, slot: 0 },
                     Target { node: 4, slot: 1 }, // price into the broker
-                ],
-            }],
+                ])],
             edges: vec![
                 Edge { from: 0, to: 2, slot: 0, from_field: 0 },
                 Edge { from: 1, to: 2, slot: 1, from_field: 0 },
diff --git a/crates/aura-engine/tests/ger40_breakout.rs b/crates/aura-engine/tests/ger40_breakout.rs
index 1f5eda0..1759899 100644
--- a/crates/aura-engine/tests/ger40_breakout.rs
+++ b/crates/aura-engine/tests/ger40_breakout.rs
@@ -165,10 +165,7 @@ fn build_harness(
     // declaration order open(0), high(1), low(2), close(3) is the merge tie-break
     // order for the Barrier(0) group.
     let sources = (0..4)
-        .map(|slot| SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![Target { node: RESAMPLE, slot }],
-        })
+        .map(|slot| SourceSpec::raw(ScalarKind::F64, vec![Target { node: RESAMPLE, slot }]))
         .collect();
 
     Harness::bootstrap(FlatGraph { nodes, signatures, sources, edges }).expect("valid strategy DAG")
diff --git a/crates/aura-ingest/examples/shared/breakout_real.rs b/crates/aura-ingest/examples/shared/breakout_real.rs
index 46e546c..6d1788f 100644
--- a/crates/aura-ingest/examples/shared/breakout_real.rs
+++ b/crates/aura-ingest/examples/shared/breakout_real.rs
@@ -184,10 +184,7 @@ pub fn build_harness() -> (Harness, Taps) {
     // declaration order open(0), high(1), low(2), close(3) is the merge tie-break
     // order for the Barrier(0) group — identical to the synthetic capstone.
     let sources = (0..4)
-        .map(|slot| SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![Target { node: RESAMPLE, slot }],
-        })
+        .map(|slot| SourceSpec::raw(ScalarKind::F64, vec![Target { node: RESAMPLE, slot }]))
         .collect();
 
     let h = Harness::bootstrap(FlatGraph { nodes, signatures, sources, edges })
diff --git a/crates/aura-ingest/tests/real_bars.rs b/crates/aura-ingest/tests/real_bars.rs
index 2f36c58..d74a2d8 100644
--- a/crates/aura-ingest/tests/real_bars.rs
+++ b/crates/aura-ingest/tests/real_bars.rs
@@ -47,14 +47,11 @@ fn run_sample_over(prices: Vec<(Timestamp, Scalar)>) -> RunReport {
             f64_recorder_sig(),
             f64_recorder_sig(),
         ],
-        sources: vec![SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![
+        sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                 Target { node: 0, slot: 0 },
                 Target { node: 1, slot: 0 },
                 Target { node: 4, slot: 1 }, // price into the broker
-            ],
-        }],
+            ])],
         edges: vec![
             Edge { from: 0, to: 2, slot: 0, from_field: 0 },
             Edge { from: 1, to: 2, slot: 1, from_field: 0 },
diff --git a/crates/aura-ingest/tests/streaming_seam.rs b/crates/aura-ingest/tests/streaming_seam.rs
index 2ddaefa..941f328 100644
--- a/crates/aura-ingest/tests/streaming_seam.rs
+++ b/crates/aura-ingest/tests/streaming_seam.rs
@@ -53,14 +53,11 @@ fn run_sample(window: (Timestamp, Timestamp), source: Box<dyn Source>) -> RunRep
             f64_recorder_sig(),
             f64_recorder_sig(),
         ],
-        sources: vec![SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![
+        sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                 Target { node: 0, slot: 0 },
                 Target { node: 1, slot: 0 },
                 Target { node: 4, slot: 1 },
-            ],
-        }],
+            ])],
         edges: vec![
             Edge { from: 0, to: 2, slot: 0, from_field: 0 },
             Edge { from: 1, to: 2, slot: 1, from_field: 0 },